Preparation of acrylonitrile



United States Patent 3,206,499 PREPARATION OF ACRYLONITRILE George E.Ham, Lake Jackson, Tex., assignor to The Dow Chemical Company, Midland,Mich., a corporation of Delaware N0 Drawing. Filed Jan. 10, 1962, Ser.No. 165,319 1 Claim. (Cl. 260-4659) This invention relates to a newprocess for the preparation of acrylonitrile from 1,2-difunct1'onalethane derivatives.

It is known that alkali metal cyanides react with 1,2- difunctionalethane derivatives such as ethylene dichloride to make succinonitrile.It is also known that hydrogen cyanide and ethylene dichloride react atvery high temperatures in the gaseous phase to make the intermediate3-chloropropionitrile which dehydrochlorinates under these conditions toacrylonitrile.

It has now been found that in the reaction of an alkali metal cyanidewith a 1,2-difunctional ethane compound such as ethylene dichloride,acrylonitrile is formed as an intermediate product according to theequation It has also been found that by carrying out the reaction undersuitable conditions of temperature and pressure, the intermediateacrylonitrile can be separated by distillation from the reaction mixturesubstantially as it is formed, thereby preventing the further progressof the reaction toward the production of succinonitrile. It has beendetermined that carrying out the reaction at about 50 C. to about 200 C.and under atmospheric or subatmospheric pressure enables the productionand separation of acrylonitrile as a major product of the process.

The 1,3-difunctional ethane derivatives which are operable in thisprocess are those compounds represented by the formula where X and Y areradicals capable of replacement by a cyanide group to make thecorresponding nitrile upon reaction with an inorganic cyanide. Thesymbols X and Y, therefore, stand for radicals such as halogen, wherehalogen means chlorine, bromine, or iodine, and sulfonate or sulfateester groups of the formula RSO30 or ROSO O- respectively, R being anorganic radical. The groups X and Y may be similar, that is, X may bebromine and Y chlorine, or both X and Y may be bromine, or both may besulfonate, or they may be dissimilar, for example, X may be chlorine andY a sulfonate group, or X may be bromine and Y a sulfate ester group.Representative compounds thereby represented are the ethylene dihalides,2-haloethane alkyl or aryl sulfonates, ethylene bis(arylsulfonates), andsulfate esters similar to the sulfonates named. Particularly adapted tothis process are the bis(2-haloethyl) sulfates.

Preferably, the process is operated by adding finely divided solidalkali metal cyanide to a solution of the 1,2- disubstituted ethane in asuitable inert solvent at a temperature between about 50 C. and about200 C. and under a pressure no higher than atmosepheric pressure, i.e.,760 mm. of Hg, the conditions of the reaction being such that theacrylonitrile is distilled from the mixture more or less as it isproduced. The distillate consists of acrylonitrile, hydrogen cyanide,and varying amounts of 1,2-disubstituted ethane and solvent dependingupon their boiling points. Acrylonitrile is ordinarily separated fromthe condensed mixture by distillation.

By alkali metal is meant any of Group 1A of the periodic table ofelements, this group comprising lithium,

sodium, potassium, and rubidium. Sodium cyanide is preferred for itslower cost.

Because the the critical point of this new process is the speed withwhich acrylonitrile can be removed from the reaction mixture, the1,2-disubstituted ethane and the reaction solvent, if any, are bothadvantageously selected from those having boiling points substantiallyabove that of the desired product. Thus, a good yield of acrylonitrileis more easily obtained when ethylene dibromide is used as a reactantrather than the lower boiling ethylene dichloride. Similarly, reactionsolvents having boiling points Well above the boiling points ofacrylonitrile are preferred for the same reason. Such higher boiling reactants and solvents also avoid undue dilution of the product in thedistillate. Solvents suitable for use in the process are those which canbe used in the general reaction.

wherein M is alkali metal and R and X are as defined above. Thesesolvents include lower aliphatic alcohols, ethylene glycol ethers, loweraliphatic nitriles, dimethylformamide, dimethyl sulfoxide, and solventsof similar nature. A minor amount of Water may be included with thesolvent. For the reasons explained above, solvents of the above grouphaving boiling points above C. are preferred.

The pressure and temperature levels at which the process is to beoperated are chosen from the ranges shown above taking intoconsideration the boiling points of the materials involved and thedesirability of keeping the proportion of acrylonitrile in thedistillate as high as practically possible. A pressure of about 1-200mm. Hg absolute and a reaction temperature of about 75-150 C. arepreferred. Obviously, the reaction temperature must be above the boilingpoint of acrylonitrile at the pressure chosen.

The ratio of reactants is not a critical point, but preferably a ratioof from about the stoichiometric one mole to about 20 moles of1,2-disubstituted ethane to two moles of cyanide is used. Most preferredis an excess of 1,2- disubstituted ethane in the range of about 24 molesper mole of cyanide.

The following examples illustrate ways in which the principle of theinvention has been applied but are not to be construed as limiting thescope thereof.

Example 1 Into a one liter reaction flask equipped with a thermometer, astirrer, a tube through which solids could be added, and connected to adistillation column vented through a Dry Ice trap, was put 500 ml. ofdimethyl sulfoxide and 99.0 g. (1.0 g. mole) of ethylene dichloride. Themixture was heated to C. and the pressure on the system was lowereduntil refluxing began in the distillation column head. One half grammole of solid sodium cyanide was then added in small portions to theboiling mixture over a period of 45 minutes. After the cyanide additionwas complete, the pressure was lowered further and heating at 100 C. wascontinued until there Was I nothing more passing into the Dry Ice trap.From the trap there was obtained 81.0 g. of liquid which was found onanalysis to contain 0.016 g. mole of acrylonitrile.

Example 2 In the manner described in Example 1, 1.0 g. mole ofl-bromo-Z-chloroethane was reacted with 0.50 g. mole of solid sodiumcyanide over a period of 66 minutes at IOU-120 C. with the reactionsystem under a pressure of mm. Hg absolute. The distillate contained0.112 g. mole of acrylonitrile representing a yield of 44.8%

based on the sodium cyanide used.

Example 3 In the manner described in Example 1, 1.0 g. mole of ethylenedibromide was reacted with 050 g. mole of solid sodium cyanide in 32absolute pressure of 74 mm. There was obtained 0.206 g. mole ofacrylonitrile, a yield of 82.4% of the theoretical based on the startingsodium cyanide.

Using a procedure similar to that shown in, the above examples, sodiumcyanide or another alkali metal cyanide may be reacted with compoundssuch as 2-chlor0ethyl benezenesulfonate, 2-bromoethy1 ethanesulfonate,ethylene bis(benzenesulfonate), l-bromO-Z-iodoethane, ethylene diiodide,ethylene dibromide,'ethylene brornochloride, bis(2-chloroethyl) sulfate,or bis(2-bromoetl1yl) sulfate to make acrylonitrile.

I claim:

A process for making acrylonitrile which comprises reacting bycontacting one mole of alkali metal cyanide with minutes at 100 C. underan 4 from about 0.5 to about 10 moles of a compound having the structureX--CH CH --Y where X and Y are halogen of atomic number 17-53 inclusivein the presence of an inert solvent under 1-200 mm. Hg absolute pressureat about 75 C. to about 150 C., thereby separating by distillingarcylonitrile substan tially as it is formed.

References Cited by the Examiner UNITED STATES PATENTS 2,211,240 8/40Macallum 260-465.8 2,429,450 10/ 47 Harris 260-265.9 2,467,373 4/49Dutcher et a1. 2604-4659 CHARLES B. PARKER, Primary Examiner. LEONZITVER, IRVING MARCUS, Examiners.

